In recent years, optical disc apparatuses for recording and reproduction on optical discs such as a DVD have become widespread. In the production of an optical pickup used for such an optical disc apparatus, precise bonding is necessary between a light source and a connection base for holding the light source. The following will describe a conventional bonding method.
FIG. 5A is a perspective view showing a connection base for holding a light source for an optical pickup. FIG. 5B is a perspective view showing the light source for an optical pickup. As shown in FIGS. 5A and 5B, a connection base 1 includes joints 11 and 12 which are bonded to a light source 2, and the light source 2 includes side portions 21 and 22 which are bonded to the connection base 1. The connection base 1 and the light source 2 are bonded together as follows: the components are adjusted to predetermined positions, a solder material is supplied onto the joints 11 and 12 of the connection base 1 and irradiated with laser light, and the joints 11 and 12 and the side portions 21 and 22 are soldered.
FIG. 6A is a front view showing a state after the connection base and the light source are bonded together by the conventional bonding method. FIG. 6B is a bottom plan view showing the state after the connection base and the light source are bonded together by the conventional bonding method. Conventionally, as shown in FIGS. 6A and 6B, solder 3 is set in contact with the outer edges of the light source 2 and the solder 3 is set on corners formed by the joints 11 and 12 of the connection base 1 and the side portions 21 and 22 of the light source 2 (For example, see Japanese Patent Laid-Open No. 2005-166157).
However, the conventional bonding method has the following problem: heat is applied to melt the solder material and bond the light source and the connection base, and at this point, the heat is also applied to the light source and the connection base, so that members making up the light source and the connection base thermally expand. In this case, the direction of thermal expansion varies among the members making up the light source and the connection base because the material, the shape, the holding method and so on are different among the members. Thus the relative position between the light source and the connection base is shifted. Since die casting is used for the connection base, internal residual stress is released when heat is applied by solder bonding, so that the relative position between the light source and the connection base is shifted. When a bonding interface between the light source and the connection base has a large friction force during the shift of the relative position, a return position at a temperature decrease after soldering greatly varies.
As described above, the conventional bonding method causes a wide range of variations in the relative position between the light source and the connection base, so that the characteristics of a product cannot be ensured.